Multi-range expansion material



Sept. `26, 1961 s. vERNx-:T ETAL l 3,001,401

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AMBIENT United States Patent O 3,001,401 MULTI-RAN GE EXPANSION MATERIAL Sergius Vernet, James Fay Corwin, and George Asakawa, Yellow Springs, Ohio, assignors, by direct and mesne assignments, to Antioch College, Yellow Springs, Ohio,

`a corporation of Ohio Filed July 11, 1956, Ser. No. 597,293 8 Claims. (Cl. 73-358) kThis invention relates to thermally expansible materials, and to power elements of the type disclosed in copending patent applications, Serial No. 551,829 iiled on December 8, 1955,-and Serial No. 510,078 tiled on May 24, 1955, now abandoned. Such power elements are. commonly employed to operate switches and valves. Y Objects of the invention are to `provide power elements employing solid to liquid type expansion materials; wherein the expansion materials have good resistance to chemical decomposition at elevated temperatures, and the expansion materials include mixtures of materials which in some instances undergo a plurality of'separate relatively l-arge expansions in a temperature range from about 200"Y F. to about 300 YF. y

Other objects of this invention will appear in the `following description and appended claims, reference being hadto the accompanying drawings forming a part of this specification `wherein like reference characters designate corresponding parts in the several views.

InAthe drawings:

FIG..1 is asectional view through a power element incorporating the invention. p

FIG. 2 is a performancepchart utilizing a paraffin wax; wherein the position of the power element piston is plotted against ambient temperature.

i FIG. V3 is a performance chart of a .power element utilizing 50%v paraffin wax and 50% tetrachlorobenzene.

FIG..4 is a performance chart of apower element utilizing 37% paraffin wax and 63% tetrachlorobenzene.

FIG. 5 is a1 performance chart of a powerA element utilizing 25% paraiiin wax and 75% tetrachlorobenzene.

Before explaining the present invention in detail, it is to be understood that the'invention is not limited in'its application to the details ofconstruction and` arrangement of0 parts illustrated in the accompanying drawings, since the invention is capable of. other embodiments and of ,being practiced or carried outin various ways. Also, itis to be understood that the phraseology or terminology employedherein is for the purpose oli/description Vand not of limitation. `g .v

*In the drawings thereis shown Ya power element '1including a casing 2, a body or pellet of thermally expansible material 3, a movable wall or piston 4, a corrugated stainless steel diaphragm 5, and a body of pliable forcetransmitting material 6. Material 6 is preferably the pliable material disclosed in copending application, Serial No. 583,881, tiled May 9, 1956. A disc 7 of polytetralluoroethylene `is positioned between material 6 and piston 4 in order to prevent material 6 from extruding into the clearance space 9 between piston 4 and bore 8. A spring (not shown) is provided for returning piston 4 to its illustrated position during contractive movement of material 3.

Operation of the power element is such that during temperature increase in ambient atmosphere 10 material 3 expands against diaphragm 5 so as to force material 6 upwardly in bore 8 and thereby propel piston 4 outwardly against the aforementioned spring. During temperature decrease in atmosphere 10 material 3 contracts so as to allow the spring to return piston 4 downwardly to its illustrated position.

Material 3 is preferably a straight chain paraiiin wax having a molecular weight above 400 or a mixture of said of fa Y power v element wax with l,2,4,5 tetrachlorobenzene. vPreferably discrete-particles of a .good heat conductor such as copper are dispersed throughV material 3 to quickly and evenly transmit heat through the pellet. 1 f

FIG. 2 illustrates the performance of the power` element when material 3 is composed entirely of a straight chain parain wax having a molecular weight above 400. This straight chain paran wax gives a comparatively large total expansion, which for many applications is very desirable. The large total expansion is believed to be due primarily to the straight chain character of the wax. Branched chain paraffin waxes tend to give lower total expansions because the branches on the chains are believed to interfere with one another so as to produce a rather loosely packed molecular arrangement when the wax is in the solid state; as a result of this loose molecular packing a relatively small number of molecules are available for expansion, and the total volumetric expansion is therefore relatively low. The straight chain molecules on the other hand do not obstruct one another, and they therefore tend to pack closely together in the solid state so as to give a comparatively highvolumetric expansion during temperature increase.

There is an advantage in using straight chain waxes with molecular weights above 400. vIt has beenY found that when mixtures of lower molecular weight waxes (i.e. around values of 200) are employed. the melting point tends to be undesirably depressed (as compared with the melting points of the component waxes in their pure state) when there is a substantial variation in the chainY length of the component .waxesgalso the expansion characteristics of suchlow molecular weight mixtures are poor. Y.'Ihe undesired characteristics appear to be a function of the variation in chain length as compared with the lengths of the chains. When mixtures of high molecular weight waxes are employed the effect of variation in chain length is relatively slight because of the relatively long length chains. The straight chain paraflin waxes with ,molecular Weights above 400 have the yfurther advantage that they are much more resistant to chemical decomposition at elevated temperatures than thefbranched chain paraffin waxes. Y 4 Y y FIG. 3 illustrates the performance of the power -,element when material 3 is composed of a mixture of 50% 1 by weight straight chain wax having a molecular weight above 400 and 50% by weight of 1,2,4,5-tetrachloroben^- zene. The molecular shape of tetrachlorobenzene would seem tov prevent it from mixing vsatisfactorilywith ,the paratln wax. Yet, as indicated `by FIG.' 3fan equal weight mixture of the two materials produces a relatively large total expansion over a relatively small temperature range. Additionally the hysteresis is rela-tively low at the higher temperatures. The term. hysteresis will be understood as a measure of the expansion materials ability to contract immediately when the ambient temperature is initially increased and then decreased. During temperature increase material 3 expands substantially in ,accordance with the position of piston 4 as indicated by line 12 in FIG. 3. During temperature decrease material 3 follows substantially along line 13. In FIG. 3 only about a two degree decrease in temperature is required to transfer material 3 from line 12 to line 13, whereas in FIG. Zan eleven degree decrease in temperature (see arrows 14) is required to transfer material 3 from line 12 to line 13. In otherwords the FIG. 3 material has about a two degree hysteresis and the FIG. 2 material has about an eleven degree hysteresis (at the upper end of the curve). This difference in the hysteresis is believed to be due primarily to the fact that the FIG. 2 material is a pure material, whereas the FIG. 3 material is a mixture of different materials. Apparently the pure material undergoes Patented Sept. 26,v 1961 g a certain amount of supercooling during temperature de:u

crease, whereas the mixture of materials provides seed crystals to prevent such supercooling. Thus the tetrachlorebenzene crystals are thought to act as seeding crystals for thewax.

It was mentioned earlier that logically the tetrachlorovbenzene should" not mix satisfactorily with the wax. Yet,

as can be seen from FIG. 3, an equal weight mixture of i the two materials produces avery smooth, steep expansion curve with a relatively large total expansion; It is, believed that the wax molecules form crystals and the tetrachlorobenzenemolecules forrn other crystals so` as to pro- Vvide an eutectic type crystalline material; i.e. aV material wherein crystals of wax existseparately from crystals of tetrachlorobenzen'e, with each type of crystalI insoluble in the. other and with no molecular mixing of the wax molecules kand tetrachlorobenzene molecules. Apl Weight above 40d and 63% by weight of 1,2,4,5` tetrachlorobenzene.

stages 'gives the power element two relatively st ejep but The existence of two separate melting separate motions; i.e. a tirstrelatively steep motion be- -tween 210 and 230, ancla'secondrrelatively steep'motionbetween about 250 and 280.

FIG. 5"illustrates the performance of the power element when material 3 is composed of a mixture of '2'5% We claim: y s 1. A power element comprising a container and con nected sleeve; thermally expansible material within said container; Ia metal diaphragm sealing the expansible material in the container; a piston in said sleeve; and a forcei transmitting material-between the diaphragm and piston;

said force-transmitting material being operable at` teniperatures in the neighborhoodof 250 F.; and said` thermally expansible material being amixture off 1,2,4,5 tetrachlorobenzene and a straight chain paraiiin wax having a molecular weight above 400, the tetrachlorobenzene and paraffin Wax each accounting for a substantial percentageV of the weight of the thermally expansible material.

2. The combination of claim 1 wherein the tetrachlorobenzene and wax each account for about one-halj the l weight of the thermally expansible material. n

3. The combination of claim 1 wherein the tetrachlorobenzene accounts for about63% ofthe Weight of the thermally expansible material.

4. The combination Vof claim 1 wherein the tetrachlorobenzene accounts for about 75% of the weight of the thermallyY expansible material.

,by weight straight chain parain Wax having a molecular -x 'Weight Vabove V40() and 75% of 1,2,4, 5 tetrael11orobenzene. ,This mixture gives substantially vthe same type performance curve as theFIG. 3 material. Y f

During the foregoing speciication the expansion mavterials have been described with reference to their use in power elements of the typewhich areresponsive to ambientv temperature change. "-It is contemplatedrhowever that the expansion materials could be employed with powerelements of the type which are responsive to variations inelectric current, .as for example the power elements disclosed in aforementioned application, Serial No. 551,829. It will be understood therefore that the term "power elemen as used herein refers to both temperaturefresponsivevmechanisms and electrie current res'p'gionf sive mechanisms.

5. A thermostatic power element component'formed asl a solid' three dimensional expansion pellet; said pellet comprising expansion material and a network of heat conducting material extending substantially evenly therein; said expansion material being formed as a mixture of 1,2,4,5 tetrachlorobenzene andV a straight chain paraiiin wax having amolecular Weight above 400, the tetrachloro.h benzene and wax each accounting for a substantialY percentage of thev weight of the expansion material.

6. A combination of clairn-5 wherein the tetrachloro benzene andV wax each account yfor about one-half the weightV of. thermally expansible material. s

7. `Af combinationofv claim 5, wherein the tetrachlorof Ybenzene accountsy Yforv about 63% of the weight of the thermally expansible material.

8. The combination ofA claim, 5 wherein the tetrachlorobenzene accounts for aboutf%v of the weight of the thermally expansible material. Y

ReferencesV Cited in the lile of this` patent UNITED STATES PATENTS v 2,115,502 Vernet Apr. 26, 1938 2,169,872y Clark -..s Aug. 15,1939 2,214,877. cm1; -1., sept. 17, 1940 2,259,846 Vernet 1-a Oct; 21, 1941 2,368,181. Vernet a Ian, 30, '1945 2,534,497 Albright 2, Dec. 19,1950 2,598,351 Carter ..v. May Z7. i19,52 2,668,140 Arabian Peb..2, 1954' 2,847,033 Baker -1 Aug. 12, 1958 @STM 

